Lifepo4 vs Lithium-Ion: The Battle of the Batteries

589 Published by BSLBATT Apr 19,2024

Lithium-ion (Li-ion) and lithium iron phosphate (LiFePO4) are two of the most popular types of rechargeable lithium-ion batteries used in consumer electronics and electric vehicles today.

Both offer high energy density, low self-discharge, high cell voltage, and low maintenance compared to other rechargeable battery chemistries.

However, there are some key differences between the two that make each better suited for certain applications.

lithium-ion

Li-ion batteries use lithium cobalt oxide (LiCoO2) or other lithium metal oxides as the positive electrode and graphite carbon as the negative electrode.

During discharge, lithium ions move from the positive electrode to the negative electrode through the electrolyte and separator diaphragm.

Charging reverses the flow of ions. Li-ion batteries have high energy density but can be unstable due to the highly reactive cobalt cathode.

Lifepo4

LiFePO4 batteries replace the cobalt oxide cathode with lithium iron phosphate (LiFePO4), which is more structurally and thermally stable.

This makes LiFePO4 inherently safer than Li-ion, at a cost of slightly lower energy density.

LiFePO4 also offers longer cycle life and better performance at higher temperatures.

Both types of lithium-ion batteries are common today for consumer electronics, power tools, electric vehicles, and energy storage systems. We’ll explore the key differences between them in more detail.

Chemistry

LiFePO4 batteries have a cathode made of lithium iron phosphate (LiFePO4), whereas traditional lithium-ion batteries use lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt oxide (NMC), or other metal oxide cathodes.

The key difference lies in the cathode material. LiFePO4 provides a more stable, safer cathode chemistry compared to the metal oxide cathodes found in regular lithium-ion batteries.

The iron phosphate structure resists oxygen loss, even when overcharged or shorted out. This makes LiFePO4 inherently non-combustible and eliminates the risk of thermal runaway.

In contrast, lithium-ion batteries with cobalt, nickel, and manganese cathodes can release oxygen if overcharged or damaged, leading to fires and explosions.

The layered oxide structure lacks the stability of the olivine phosphate structure in LiFePO4. This fundamental difference in cathode chemistry is what gives LiFePO4 batteries their excellent safety reputation.

Voltage

LiFePO4 batteries have a lower nominal voltage compared to lithium-ion batteries. LiFePO4 operates at around 3.2V, whereas lithium-ion batteries typically operate between 3.6-3.7V.

This lower voltage in LiFePO4 comes from the chemistry of the cathode material. LiFePO4 cathode has a flat voltage profile and can only release one electron per formula unit during charging and discharging.

In contrast, lithium-ion cathodes like lithium cobalt oxide (LiCoO2) can release most of their lithium ions, enabling higher voltages.

The lower voltage of LiFePO4 means more cells need to be connected in series to achieve the desired system voltage.

However, the lower voltage also provides some advantages in safety and stability compared to higher voltage lithium-ion chemistries.

Overall, the slightly lower voltage of LiFePO4 is a tradeoff that allows for excellent cycling stability and safety.

Charge/Discharge

LiFePO4 batteries have a very flat discharge curve compared to lithium-ion batteries.

This means the voltage output remains more consistent as the battery discharges. Lithium-ion batteries, on the other hand, have a sloping discharge curve so the voltage gradually decreases as the battery drains.

The flat discharge curve of LiFePO4 makes them ideal for applications that require stable voltage output.

Things like motor controllers and inverters benefit from the consistent voltage supply during discharge. With lithium-ion you may experience decreasing performance as the voltage drops.

LiFePO4 also charges differently than lithium-ion. The voltage climbs rapidly to about 3.65V and then remains there while the battery charges fully.

Lithium-ion voltage steadily increases throughout the charging process. This means LiFePO4 can utilize fast charging better than lithium-ion in most cases.

So in summary, LiFePO4 provides flat voltage discharge while lithium-ion is gradually sloping. And LiFePO4 charges rapidly to peak voltage while lithium-ion climbs slowly.

These discharge/charge characteristics make LiFePO4 favorable for applications needing stable voltage and fast charging ability.

Cycle Life

LiFePO4 batteries have a significantly longer cycle life compared to lithium-ion batteries.

Whereas lithium-ion may last 500-1000 cycles before degrading to 80% capacity, LiFePO4 can typically achieve 2000-5000 cycles or more. Some LiFePO4 cells have been tested to over 10,000 cycles with minimal capacity loss.

The key reason for this extended cycle life is the olivine crystal structure of the cathode material in LiFePO4.

This structure allows lithium ions to insert and extract with less stress and strain compared to layered oxide cathodes like lithium cobalt oxide.

The rigid structure of LiFePO4 does not expand or contract much during cycling, leading to greater stability over thousands of cycles.

In contrast, the layered structure of conventional lithium-ion cathodes changes shape more dramatically during cycling as lithium ions are added and removed.

This puts more physical strain on the electrodes and electrolyte, resulting in faster degradation of the battery over time.

So for applications requiring thousands of cycles over many years, like renewable energy storage or electric vehicles, LiFePO4 is the clear winner over normal lithium-ion batteries when it comes to cycle life.

The ability to withstand 3-10 times more cycles before failure makes LiFePO4 an attractive choice whenever long-term durability and lifetime are critical factors.

Safety

LiFePO4 batteries are inherently safer than lithium-ion batteries. This is due to the chemical structure and properties of the cathode material.

Lithium-ion batteries typically use cathode materials like lithium cobalt oxide (LiCoO2) or lithium nickel manganese cobalt oxide (NMC).

These layered oxide cathode materials are unstable, especially when overcharged or short-circuited.

This can lead to oxygen release from the cathode and trigger thermal runaway, resulting in fires or explosions.

In contrast, LiFePO4 has an olivine crystal structure that is very stable, even under abuse conditions.

The strong covalent bonds in the phosphate framework make it extremely difficult for oxygen to be released.

As a result, LiFePO4 does not easily go into thermal runaway and is far less prone to catch fire or explode.

LiFePO4 can withstand much higher temperatures (up to 700°F) before breaking down compared to lithium-ion’s relatively low thermal runaway temperature.

Short circuits, overcharging, and other electrical or mechanical abuse is far less likely to result in catastrophic failure with LiFePO4.

This inherent safety and stability is a major reason LiFePO4 is preferred for electric vehicles and other applications where safety is critical.

Cost

LiFePO4 batteries are generally cheaper per kWh than lithium-ion batteries.

This is because LiFePO4 uses iron phosphate as the cathode material, which is abundant and inexpensive compared to the cobalt, nickel, and manganese used in lithium-ion cathodes.

Additionally, LiFePO4 has a flatter discharge curve than lithium-ion, allowing it to use less battery management system electronics.

The simpler battery management system further reduces costs for LiFePO4.

In terms of upfront battery pack costs, LiFePO4 batteries range from $300-500 per kWh, while lithium-ion packs are $150-300 per kWh.

However, the longer cycle life of LiFePO4 compared to lithium-ion means the cost per cycle or cost over the battery lifetime is lower for LiFePO4.

Overall, the cheaper raw material costs and simpler electronics result in LiFePO4 having a lower lifetime cost per kWh despite the higher upfront cost.

This makes it an attractive choice over lithium-ion for many applications, especially where long cycle life and safety are priorities.

Applications

LiFePO4 and lithium-ion batteries are both used in a wide variety of applications, but they each have advantages that make them better suited for certain use cases.

LiFePO4 batteries tend to be preferred for high power applications like power tools and electric vehicles.

Their safe chemistry and ability to deliver high currents makes them a good fit for things that need a lot of instant power. LiFePO4 packs a punch when you need the power right away.

Lithium-ion batteries, on the other hand, are often better for smaller electronics like laptops, cell phones, and tablets.

Their higher energy density means they can store more power in a smaller, lighter package.

This makes lithium-ion great when you need to optimize for space and weight, like in a smartphone.

The tradeoff is they don’t handle high power draw as well.

LiFePO4 is ideal for high power tools, electric vehicles, and other applications that require pulsing a lot of current. Their safe chemistry also makes them well-suited for medical devices.

Lithium-ion is better for consumer electronics and other applications focused on light weight and small size. Their higher energy density is perfect for maximizing run-time.

Each technology has strengths in different applications based on the specific needs and tradeoffs. LiFePO4 for raw power, lithium-ion when space and weight are critical.

Environmental

LiFePO4 batteries have a clear environmental advantage over traditional lithium-ion batteries.

The cathode material in LiFePO4 batteries uses iron phosphate, which is not toxic and abundant in nature.

In contrast, the cobalt, nickel, and manganese used in lithium-ion cathodes are rarer elements that can be hazardous in high concentrations.

During battery production, the synthesis of LiFePO4 emits minimal greenhouse gases compared to lithium-ion.

Disposal is also less problematic, as the iron phosphate does not leach toxic chemicals into the environment.

Overall, the materials and manufacturing of LiFePO4 batteries have a much lower environmental impact.

As electric vehicles and energy storage systems grow in popularity, the choice of battery chemistry will have major ecological effects.

Widespread adoption of LiFePO4 could significantly reduce the environmental footprint of these technologies.

With their improved sustainability and safety, LiFePO4 batteries are likely to play a leading role in the green energy transition.

Conclusion

When evaluating LiFePO4 vs lithium-ion batteries, there are some key differences to consider.

LiFePO4 batteries have a lower energy density but better thermal and chemical stability.

They also have a longer cycle life, slower capacity fade, and are inherently safer.

The main downside is their lower voltage, which requires more cells in series for the same voltage as lithium-ion.

Lithium-ion batteries have a higher voltage and energy density.

This allows smaller, lighter batteries for the same capacity.

However, they are less thermally stable, prone to aging effects, and can be a fire risk if not properly managed.

For applications where safety and long cycle life are critical like electric vehicles and energy storage, LiFePO4 is usually the better choice despite its larger size and weight.

For consumer electronics where small size is most important, lithium-ion is preferable.

Though for applications in between, there are tradeoffs to consider.

Overall, LiFePO4 is the safer, longer lasting battery chemistry but gives up some performance compared to lithium-ion.

So choose lithium-ion when optimizing for energy density and LiFePO4 when optimizing for safety and cycle life. Consider the priorities for your specific application.